Currently most foreign made vehicles have separate rear stop light and turn light circuits. They either use separate filaments of the same bulb or separate bulbs, i.e. on each side there is one independent bulb or filament for the brake signal and one for turn indication. Most United States made vehicles use the same bulb and filaments for both functions. When a trailer with a lighting system compatible for connection to a United States made vehicle is used with a foreign made vehicle normally the turn and stop light signals cannot be utilized together; either stop or turn signals individually but not both systems. If both stop and turn signal circuits are connected and the brakes are applied, the towing vehicle brake lights, the trailer signal lights, and the towing vehicle turn lights come on. This results in six additional lights being added to the towing vehicle's normal stop light circuit; two on the trailer and the four (two in front and two in the rear) direction indication lights on the towing vehicle. The stop signal, as a result, will be only a dim glow and ineffective, since the circuit is overloaded. Similarly if the turn signal is activated, since in the brake circuits the left and right lights are tied together and the trailer lights tie the towing vehicle turn and brake circuits respectively together, six lights are added to the towing vehicle's normal turn light circuit, overloading the circuit; two trailer lights, two towing vehicle stop lights, and the front and rear turn lights on the towing vehicle on the side opposite the turn direction. Consequently all of the stop and direction lights on the trailer and towing vehicle flash dimly if at all, and no direction is indicated. If the brakes are applied while the turn signal is on, only a dim to slightly dimmer flashing of all lights occurs. Diodes have been inserted in the connection wires to the trailer lights as a remedy, but this only partially solves the problem. The turn and brake signals can be used separately but when the brakes are applied while turning, the brake signal overrides the turn signal and no directional indication is given. Since the brakes are typically applied while waiting to turn or during a turn the loss of the direction signal on the trailer creates a hazardous condition. The trailer signal light adapter circuit is interposed between the towing vehicle circuit and the trailer circuit to give full signal operation at all times, alleviating the above-mentioned problems.